The problem of simulating light transport in participating media has been extensively studied. One aspect is the problem of efficiently computing the single scattering component from point light sources, including spotlights. Such light sources account for most dramatic high frequency lighting effects, such as light beams and volumetric shadowing. In addition, such light sources serve as a significant source of noise in homogeneous media because the other aspect, the transmission term, is generally nonzero and smoothly varying, and thus comparatively non-noisy.
Previous work in unbiased volume rendering has concentrated on efficient importance sampling of the transmission term. In one approach, the single scattering integral is estimated by jittered ray marching with a uniform step size Δx. As an improvement, this step size can be made adaptive by responding to local changes in the illumination, or by making the same a function of the extinction coefficient.
Nevertheless, such solutions require significant computational efforts and time. Consequently, there remains a need for a better way to perform such rendering.